Remove XHR from pending JS on exception

tests/behat/app_behat_runtime.js

@@ -98,6 +98,7 @@
         var index = requestIndex++;
         var key = 'httprequest-' + index;
 
+        try {
             // Add to the list of pending requests.
             addPending(key);
 
@@ -107,6 +108,10 @@
             });
 
             return realOpen.apply(this, arguments);
+        } catch (e) {
+            removePending(key);
+            throw e;
+        }
     };
 
     var waitingBlocked = false;